It is known to use epxansion joints within concrete floorings, to take into account thermal expansionretraction of the concrete. Indeed, there must be provided means whereby some level of horizontal relative play of adjacent concrete slabs be possible, otherwise the flooring will crack and its integrity will become at stake.
Typical prior art includes U.S. Pats. Nos. 2,171,709 issued in 1939; 3,395,507 issued in 1968; and 3,572,225 issued in early 1971. All these (expired) patents show some form of panel assembly vertically mounted between a proximate pair of concrete blocks or slabs. The panel assembly defines a compressible section whose thickness may vary in accordance with relative horizontal displacements of the slabs. These expansion joints further include a large dowel extending horizontally, so as to prevent relative vertical displacement of the slabs with respect to one another.
In the first above-mentioned patent, issued to Niel, Jr, there is shown in FIG. 3 one concrete slab being anchored to the sub-floor G by vertical anchor stakes 15, 20, while the other concrete slab is engaged by the horizontal dowel 14 which project from said one concrete slab.
One drawback of Niel, Jr's expansion joint is that the concrete will harden unto the whole of the horizontal dowel 14 (which extends through both concrete slabs), and, since the dowel is therefore integral to the two concrete slabs, further compression of the compression board sandwiched between the two slabs is impossible while displacement of the slabs away from each other will be very difficult.